Exploring Novel Immunologic or Microbiologic Mechanisms Leading to Iron Deficiency in Quiescent Pediatric Crohn’s Disease

Background: Iron deficiency anemia (IDA) is the most common extra-intestinal complication seen in patients living with inflammatory bowel disease (IBD), Given the significant impact on quality of life, anemia must be identified and corrected quickly. Oral and intravenous iron replacement therapies uniquely alter the gut microbiota in patients with IBD. Prior studies have shown the efficacy of oral iron is limited in IBD. Studies of iron absorption capacity in patients with quiescent disease reveal that patients do have the ability to absorb iron; yet it is known that 1 in 5 patients in disease-free remission may still have some measure of iron deficiency anemia on laboratory examination. Therefore, there is an urgent need to understand the etiology of iron deficiency anemia in quiescent pediatric IBD to optimize treatment. There is a lack of research evaluating the microbial, inflammatory, and immunologic factors implicated in iron malabsorption and metabolism in patients with quiescent Crohn’s disease. Given decades of research linking the pathogenesis of IBD to disruptions in the microbiome, it is hypothesized there are differences in the microbiota and immunologic response in patients with quiescent Crohn’s disease that explain the pathogenesis of IDA. Evaluation of these differences will allow for the development of a predictive model used in the treatment of IDA in pediatric Crohn’s disease. We evaluated the impact of the microbiome and immune status on iron regulation in pediatric patients with quiescent Crohn’s disease, specifically seeking to understand if altered compositions in intestinal microbiota or immune phenotypes may explain the etiology of, or mechanism for, iron deficiency anemia in this patient population. Methods: We utilized both cross-sectional, descriptive, and analytical study designs to evaluate stool and serum samples stored in the JRI Live Cell Bank (LCB). 365 samples met the initial inclusion criteria, with an additional 222 sets excluded due to absence of stored stool or due to active disease on histopathologic evaluation. Study participant characteristics were collected. 143 stored samples were included for initial 16S microbiome analysis from 56 male (39.2%) and 87 female (60.8%) study participants, aged three to twenty-one years, with biopsy confirmed, quiescent Crohn’s disease. Comparator groups included similarly matched quiescent Crohn’s disease study participants without iron deficiency anemia as well as healthy pediatric study participants with and without IDA, all of whom were represented in the JRI LCB. Results: We applied Next Generation Sequencing (NGS) and Shotgun Metagenomic Analysis to stool samples. Samples were analyzed for taxonomic composition, alpha diversity (Chao 1 index, Shannon-Wiener index, and Simpson index), and beta diversity (Bray-Curtis dissimilarity and UniFrac distance). We measured hepcidin and interleukin 6 (IL6) levels in stored serum samples. Results obtained were compared against reference datasets for healthy gut microbiome as well as that associated with iron deficiency anemia without concomitant IBD. Conclusions: To our knowledge, this is the first study to utilize microbiome analysis in quiescent pediatric Crohn’s disease with concomitant IDA to further identify etiologies of IDA in quiescent pediatric Crohn’s disease, which may then be targeted in the management of iron deficiency.